The present invention relates to a sliding member in which a high load acts on an end side of a sliding surface thereof, and particularly to a sliding member for a main bearing for supporting a crankshaft of an engine, for example.
In general, an engine used for an automobile or the like is constructed so that a crankshaft and a piston are mutually coupled via a connecting rod. This engine generates driving force by using the connecting rod to convert up-and-down movement (vertical movement) of the piston into rotational movement and to transmit it to the crankshaft. Because the crankshaft obtains the rotational movement by converting the up-and-down movement as described above, a main shaft thereof is rotated in a so-called elliptical orbit, that is, in a deflected state in an radial direction if using a grandiloquent phrase.
However, if the crankshaft is deflected during sliding operation before the main bearing supporting it conforms to the crankshaft, that is, in an initial state immediately after newly bringing it into use, a load acts particularly on both end portions in an axial direction of the main bearing. Therefore, the bearing surface load sometimes rises extremely in the portions to cause breakage of an oil film and accordingly, the sliding operation in a partial metallic contact state has caused seizure or the like. For preventing this seizure, it is necessary to improve conformability in the initial state, and in particular, to improve the initial conformability on an end side of the sliding surface in the axial direction.
There is known a sliding member which is improved in anti-seizure property by covering a bearing alloy layer with an overlay layer, by directly spraying hard particles of the mean particle diameter of 20 to 100 μm on the overlay layer to form fine recesses having a crater shape on the overlay layer working as a sliding surface, and by confining lubrication oil to the recesses, for example. See JP-A-2002-147459 (Paragraph “0010” to “0034,”, and Table 4), for example.